1. Field of the Invention
This invention relates to the bonding of cellular glass bodies and more particularly to a bonded cellular glass body system and mortar therefor wherein the mortar comprises a substantial portion of a glass powder having a composition substantially comparable to that of the cellular glass being bonded.
2. Description of the Prior Art
Acid-resistant mortars and coatings for insulating systems are well known in the art. Such mortars are generally employed in bonding insulating systems which are exposed to cyclic acidic environments. For example, in an industrial smoke stack, as in a coal burning power plant, a brick lining has been employed which brick lining was bonded with an acid-resistant silicate containing mortar. The mortar and brick were acid resistant in order to avoid damage due principally to the presence of sulfuric acid formed by hydrolysis of sulfur oxides in the stack gases.
The early acid-resistant mortars comprised wet mixtures of silica sand and sodium silicate which were cured by evaporation and exposure to acid, either as a wash, or while in service. An important development was the use of a setting agent to gel or partially gel the silicate so that mortar strength developed rapidly to permit continuous laying of brick. Additionally, the use of setting agents eliminated the need for acid washes.
Silica sol based mortars have found limited use because of the cost and poor workability. They have been used where cations are not wanted or better weatherability is desired. The present silica sol based mortars use an alkaline silicate glass as a setting agent to raise the pH and destabilize the sol. All the foregoing mortars were developed to bond dense acid-resistant brick systems and did perform very well. Brick densities were in the order of 140 pounds per cubic foot which insured sufficient pressure on the motor joint to promote a good bond. Moreover, the linear coefficients of thermal expansion of brick and prior art mortars were comparable (ca. 7-9 .times. 10.sup.-.sup.6 in/in/.degree. F.) so as to minimize spalling and thermal shock failures.
More recently, however, superior insulation compositions have been developed, particularly in the area of cellular glass type compositions. For example, cellular borosilicate glass compositions in the form of blocks or slabs have been developed which are acid resistant and which have excellent insulating properties. The cellular silicates, however, differ substantially from bricks in both physical and thermal characteristics. The cellular boro-silicate glasses have a density of only about 9 - 15 pounds per cubic foot and while being an important advantage from one standpoint, that density does not provide sufficient joint pressure to proivde a good bond with prior art mortars. Moreover, a cellular boro-silicate glass composition may typically have a linear coefficient of thermal expansion of about 1.6 .times. 10.sup.-.sup.6 in/in/.degree. F., far lower than that of bricks or prior art mortars. The low coefficient is again desirable from an application standpoint, but causes bond failures with existing mortars. Additionally, the surface of cellular glasses is not easily wet and it is difficult to "key" mortars into irregularities in the surface as there is almost no surface porosity to encourage formation of a strong glass body/mortar bond. Also, potassium or sodium silicate cements cause severe shear or failure of the bond between cellular glass bodies.
Accordingly, there is a need for acid resistant compositions useful in bonding cellular glass bodies such as bodies of cellular boro-silicate compositions. Moreover, there is a need for a mortar of the type described that is able to provide a bonded system having good thermal shock characteristics. Additionally, there is a need for acid resistant mortar compositions having thermal shock characteristics compatible with those of cellular glass boides so as to readily provide an efficient bonded glass body system useful in an acid environment. Further, there is a need for acid resistant mortar compositions that avoid shearing or failure of the bond between cellular glass bodies.
This invention provides acid resistant mortar compositions and cellular glass body systems bonded therewith which overcome the disadvantages of known mortars and systems and will be further understood as the specification proceeds.